This invention relates in general to drum support apparatus and more specifically to an improved drum supporting hub and a drum assembly including the hub.
It is generally recognized in the art that photoreceptor drum slippage between an imaging drum supporting hub and the drum it supports can significantly affect copy quality. As known in the art a uniformly charged photoreceptor coated drum is illuminated in image configuration to form an electrostatic latent image on the drum. The drum bearing the image is rotated through a developing station containing toner particles which are attracted to and deposited on the photoconductor coating in image configuration. The resulting toner image is then electrostatically transferred to a receiving sheet. The receiving-sheet bearing the toner image is then removed from the drum and transported through a fuser which fixes the toner image to the receiving sheet. Any residual toner is thereafter cleaned from the photoreceptor surface. Thus, the imaging cycle involves uniform charging, imagewise discharging, developing, transfer, and cleaning. The drum and other components of the imaging system must be synchronized to ensure quality images. The drum is driven by torque applied to the hub by means of a gear or pulley attached to the hub or shaft on which the hub is attached. For economic or space saving reasons, torque may be applied to a hub at one end of a drum and the drum itself transfers at least some of the torque to other devices by means of a gear or pulley secured to a hub at the opposite end of the drum. In addition, resistance to rotation of the drum may be generated by developer applicators, cleaning blades or brushes and the like in contact with the drum. Thus, if slippage occurs during the imaging process, it is impossible to maintain consistently high copy quality in modern, highly synchronized electrostatographic imaging systems.
A photoreceptor conventionally utilized for copiers and printers comprises a hollow electrically conductive drum substrate which has been dip coated with various coatings including at least one photoconductive coating comprising pigment particles dispersed in a film-forming binder. These drum type photoreceptors are usually supported on an electrically conductive shaft by drum supporting hubs or end flanges. The hubs are usually constructed of plastic material and have a hole through their center into which a supporting axle shaft is inserted. Since hubs are usually constructed of electrically insulating plastic material, an electrical grounding means comprising a flexible spring steel metal strip is secured to the hub and positioned to contact both the electrically conductive axle shaft and the electrically conductive metal substrate of the photoreceptor drum. One type of grounding means is illustrated in U.S. Pat. No. 4,561,763. However, these grounding means are molded or other wise attached to the side of the hub that faces the interior of the drum. Thus, when the hub is mounted in an end of the drum, the grounding means cannot be readily seen when a support shaft is inserted through the hub and drum. Thus, the grounding means can occasionally be damaged by bending when the shaft is installed. Damaged grounding strips can cause loss of electrical ground during installation of the shaft or can lead to premature failure during image cycling. Also, sufficient contact pressure between the grounding strip and the shaft or substrate is difficult to achieve. Thus, to achieve as much contact pressure as possible between the resilient plastic hub fingers and the adjacent drum substrate, expensive plastic materials are employed. Although excellent drum support is provided by these hubs, slippage between the hub and the drum substrate can still occur under high torque conditions where considerable friction is imposed on the surface of the photoreceptor by contact with subsystems such as cleaning blades and the like or where the flange on the opposite end of the photoreceptor drum is utilized to drive other copier or printer components.
Often the hub or end flange is secured to the end of the drum by a thermosetting resin adhesive. The use of an adhesive increases the number of steps and complexity of equipment required to assemble and disassemble a hub and cylindrical member assembly. Recycling of used drums having glued hubs is difficult, if not impossible, because of damage to the hub or the drum or both during removal of the hub from the drum by common techniques such as by hammering. Such removal techniques damage or destroy both the drum and the hub. Further, where disassembly is accomplished without damage, cleaning of both the hub and the cylindrical substrate is required to remove adhering adhesive. In addition, adhesive application equipment utilized during mounting of an end flange to a cylindrical substrate are difficult to maintain because the adhesive has a short pot life and often solidifies and clogs the equipment thereby requiring time consuming efforts to clean and remove the solidified adhesive. The use of bolts and nuts to secure hubs to drums requires time intensive activity.
Another type of hub avoids the need for an adhesive by utilizing resilient fingers having pointed tips that dig into and penetrate the inner surface of the drum. This hub is described in U.S. Pat. No. 5,357,321, the entire disclosure thereof being incorporated herein by reference. The hub provides excellent support for the drum. However, the pointed tips can form scratches and grooves in the interior surface of the drum during installation, use and removal. These scratches or grooves can adversely affect recycling of the cylindrical substrate. For example, in processes for dip coating a hollow cylindrical substrate such as a drum, the substrate is immersed in a coating solution by vertically moving the substrate in a direction parallel to the axis of the substrate. To avoid coating the interior of the hollow substrate, an expandable mandrel is usually employed to grip and seal off the upper end of the drum during the immersion coating process. Sealing of the upper end of the cylindrical substrate traps air within the interior of the cylindrical substrate below the mandrel during the coating operation thereby preventing any significant entry and deposition of the coating material within the hollow interior of the cylindrical substrate during the dip coating operation. However, scratches or grooves in the upper end of the interior of the cylindrical substrate interferes with the establishment of an airtight seal thereby allowing air to leak out from the interior of the cylindrical substrate past the mandrel seal. This allows undesirable entry and deposition of the coating material within the interior of the cylindrical substrate during dip coating operations. Also, the pointed tips provide a limited number of gripping points to secure the hub to the periphery of a hollow drum for high torque situations.